Microphone.



H. E, SHHEEVE.

MlCRDPHONE.

.APPUCATION FILED DEC. 26, !9l3.

7 Patented Apr. 6, 1915,

ritiri-rn enanas ramener HERBERT EDWARI) SHREEVE, OF MILBURN, 'NEW JERSEY, ASSIGNUR TO 'WESTERE ELECTRIC COMPANY, 0F NEW YORK, N. Y., A CORPORATXON 0I? ILLINOS.

MICROPHONE.

Specification of Letters Eatent.

Fatented apr d,

No. 629,261. Divided and this application nled December 2G,

191e. semi no. 808,732.

To all whom t may concern:

Be it known that HERBERT EDWARD Siinnnvn. a subject of the King of Great Britain, residing at Milburn, in the county I of Essex and State of New Jersey, have invented a certain new and useful improvement in Microphones, of which the following is a full, clear, concise, and exact description.

This invention relates to telephonie devices and more particularly to a microphonic device in ywhich the resistance var-ying medium is comininuted material retained between two relatively movable contactelements constituting Walls of a containing ehamben and is a division of my copending application, Serial Number 629,261, iiled May 25, 1h11.

The object of this' invention is to provide means in connection with Isuch a microphonic device for automatically maintaining the comminuted material in a condition for obtaining thelmost beneficial results.

,in accordance with this invention the chamber containirriz,- the comminuted material has one wall which operates by expanding and contracting toward and awa-y from thecomminui'ed material under the direct influence of Lne heat generated in the chamber to prevent packing of the comminuted material. This feature is preferably obtained by use of a thermostatic diaphragm in the chamber containing the comminuted material. Such a diaphragm may be made of plates of two metals of dissimilar coefficients of expansion and it 'has been found that gold and iron are suitable metals for this purpose.

The drawing illustrating this invention is a. cross-sectional view on an enlarged scale of a microphonic eiement.

"ris shown in the drawing, 5 designates a metal cup in which is secured a stationary electrode, preferably of carbon, which is secured to a metal button 7 having a screwthreaded stud 8 extending through the wal] of the. container 5 to receive a clamping nut 9. The metal disk Y is insulated from the wall of the chamber 5 by means of an insulating disk i@ and the clamping nut 9 is separated from the outer wall of the cham# lber by an insulating washer 1l. Secured to the front wall of the chamber' by means of a screw-threaded clamping ring 12 engaging screw threads i3 upon the wall of the chamber 5, is a diaphragm formed of two thin plates of metal 15 and 16. The inner one l5 is preferably of gold and the outer one 16 is of iron. These plates are clamped together at their outer edges between the outer margins of the chamber 5 and a flange 17 formed upon the clamping ring l2. Centrally mounted upon the diaphragm is a metal rod 20 whichinay serve as one terminal of an electric circuit when the device is used in a transmitter, or when this device is used in a repeater this member 20 may be formed of iron and constitute a pole piece to cooperate with the receiving eicment of the repeater. The microphonic element thus constructed is partly vfilled, as sho-wn, with comminuted material, preferably granular carbon, thei circuit through it being` directly from one electrode to the other. Electricai connections may be made to member 20 and an ei:- tension 22 of the screw-threaded stud S.

The action of the diaphragm formed of the two metals of dissimilar coeiiicients of expansion is such that any tendency of the comminuted material to pack will cause said diaphragm to move away from the opposing electrode, therebyrelieving the pressure and maintaining the transmitter button in a sensitive state or condition. Gold has a higher coeiiicient of expansion than iron and gives a good Vcon-tact surface for the carbon granules while iron serves asan element of the thermostat. The gold plate lying next to the comminuted material and expanding more rapidiy than the other, the diaphragm moves inwardly upon any increase in teinperature in the granular chamber and conversely moves outwardly upon decrease in the temperature. it will be see therefore that during the icw of current tl rough the ,I

resistance varying medium there is a gradual increase in temperature which will at first cause a gradual inward moving of the dias phragm. T his action, however, is followed by a tendency of the granules to pack, thus lowering the resistance and consequently detiti creasing the heating effect of the granuiar material. rihis decrease in temperature results in a cooling of the diaphragm and a consequent movement of the diaphragm ontwardly, whereupon the granules are relieved of pressure and resistance and temperature are again increased, thus causing the diaphragm to again vmove inwardly. It has been found in practice that a diaphragm 'constructed in this manner has a periodic movement forward and backward, the period being of about thirty to forty seconds duration. This movement although extremely slight and impossible of direct observation is ysufficient to keep the carbon granules in a free and sensitive state.

What I-.claim is:

l. In a microphonic device, a container for comminuted material having as `one Wall a thermostatic diaphragm arranged to bend inwardly and outwardly with varying degrees of heat generated'by the flow of current through said device.

2. In a microphonie device, comminuted material and a container therefor having as one wall a movable diaphragm composed of two plates of different coefficients of expansion and responsive to heat generated by the flow of current through said device to vary the pressure'upon' the comminuted material.

3. In a microphonic device, a container for a granular resistance varying material having asv'one wall a thermostatic diaphragm adapted to bend outwardly with decreasing temperature.

4. In a microphonic device, a container for granular resistance varying material having as one wall a-thermostatic diaphragm adapted to bend inwardly with increasing temperature and outwardly with decreasing A temperature.

- plates of gold and iron and responsive to heat generated by the flow of current through said device to vary the pressure upon the comminuted material.

In witness whereof, I hereunto subscribe.

my name this 20th day of December, A. D., 1913.

HERBERT EDWARD saumure.V

Witnesses:

ALICE HAZLEY, NANON E. TUTHILL. 

